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Scientists find tiny 'dawn runner' dinosaur

The delicate skull of Eodromaeus

The delicate skull of Eodromaeus, showing its slender sabre-shaped upper teeth, is nestled in the hands of University of Chicago paleontologist and National Geographic Explorer-in-Residence Paul Sereno. The skull is composed of replica bones.(Source: Mike Hettwer)


A fossil of the petite, two-legged Eodromaeus, which means 'dawn runner', was found in Ischigualasto, a well-explored rock formation in northwestern Argentina that has yielded hundreds of precious fossil discoveries.

Scientists say the find of two near-complete dino fossils right next to each other has helped shed light on the development of predatory dinosaurs known as theropods (which means beast-footed), including the famous T. Rex.

"It really is the earliest look we have at the long line of meat eaters that would ultimately culminate in Tyrannosaurus rex near the end of the dinosaur era," says palaeontologist Paul Sereno of University of Chicago .


Fossils of small theropods are rare, and this one measures about two meters long. Scientists believe it weighed 4.5 to 7 kilograms.

The Eodromaeus had a long neck and tail, sharp claws and biting canine teeth.

Early dinosaurs common and diverse

By examining its limbs, scientists believe they have found differences between the Eodromaeus and its contemporary, the Eoraptor, which they now believe belonged to a different family lineage, the huge, long-necked and four-legged sauropods.

Both species were about the same size and ran on two legs, suggesting that the three main types of dinosaur (ornithischians, sauropodomorphs, theropods) that lived during the late Triassic period shared similar body types.

But the newly discovered Eodromaeus had a skull that resembled other theropods, while the plant-eating Eoraptor "had more sauropod-like features, including enlarged nostrils and an inset first lower tooth," says the study's authors.

An examination of the overall fossil record from the area shows that early dinosaurs "were more common and diverse than previously thought," says the study which appears in the journal Science.

By logging thousands of fossils in the area, from lizard-like creatures to mammal-like reptiles that outnumbered the dinosaurs, scientists believe that dinosaurs likely came to dominate the landscape slowly, over several million years.

"Dinosaurs took their sweet time to dominate the scene," says lead author of the study Ricardo Martinez of Argentina's National University of San Juan .


Tags: dinosaurs, fossils, palaeontology